Microtubules are intrinsically dynamic polymers of tubulin found in all eukaryotic cells. Essential for cell division, intracellular transport, cytoplasmic organization, cell polarity, and cell motility, microtubules execute their functions by serving as tracks for the movement of motor proteins that ferry macromolecular substrates throughout the cytoplasm. In other instances, they perform mechanical work by regulating tubule length. A host of cellular proteins normally regulate microtubule function during the cell division cycle, including many that affect the polymerization state of the tubulin polymer. Typically, these proteins exploit the inherent instability of the microtubule. [unreadable] [unreadable] We helped describe a novel in vitro interaction between microtubules and the HIV-1 protein Rev in which Rev was found to rapidly depolymerize microtubules under a variety of conditions (Watts et al., 2002. J. Cell Biol. 150:349). An explanation of Rev-microtubule interactions is suggested from an amino acid sequence similarly between Rev and Kin I kinesins. These proteins are members of the kinesin superfamily distinguished by their potent microtubule destabilizing activities. [unreadable] [unreadable] The proposed research aims to identify the amino acids present in Rev that are required for microtubule binding and depolymerization. Specifically, we will mutate the residues in Rev that are shared with Kin I proteins to test the hypothesis that these proteins interact with microtubules by a common mechanism. We will compare the depolymerization activities of wildtype and mutant Rev proteins under a variety of experimental conditions including microtubules present in living cells. We are especially interested to determine whether cell cycle defects seen in cells over-expressing Rev are due to Rev-microtubule interactions. This provides the unique opportunity to assess whether Rev or Rev-derived peptides have antiproliferative activity under conditions that may be found in an HIV-infected cell. [unreadable] [unreadable]